This invention relates to spinning cells and has particular reference to spinning cells used for the coagulation of lyocell filaments.
As used herein, the term "lyocell" is defined in accordance with the definition agreed by the Bureau International pour la Standardisation de la Rayonne et de Fibres Synthetique (BISFA) namely:
"A cellulose fibre obtained by an organic solvent spinning process; it being understood that: PA1 (i) providing a blow nozzle having an exit on one side of said air gap, PA1 (ii) providing a suck nozzle having an entrance on the opposite side of said air gap to said blow nozzle, PA1 (iii) said suck nozzle having a greater cross-sectional area at its entrance than said blow nozzle has at its exit, PA1 (iv) baffle means located within said spin bath to restrict the flow of currents of liquid within said spin bath and to calm the surface of said liquid, PA1 (v) an aperture at the lower end of the spin bath through which coagulated filaments emerge in the form of a tow, PA1 (vi) a cylindrical gaiter of flexible resilient material having an orifice which in the unrestrained condition is slightly smaller in cross-sectional area than said tow, said gaiter being sealingly secured at its upper around said aperture at said lower end of said spin bath, said tow passing, in use, through said orifice and thereby expanding the cross-sectional area of said orifice, PA1 (vii) means to supply spin bath liquor to said spin bath, PA1 (ix) means to remove spin bath liquor from said spin bath, PA1 (viii) means to supply air of defined temperature and humidity to said blow nozzle. PA1 (i) providing a cross-draught of air across said air gap parallel to the surface of said mixture in said spin bath, PA1 (ii) maintaining the temperature of said air below 50.degree. C. and above the temperature which would cause freezing of water within said strands of said mixture, PA1 (iii) maintaining the relative humidity of said air providing said cross-draught below a dew point of 10.degree. C., PA1 (iv) damping the flow of liquid currents generated in said mixture in said spin bath by the passage of said strands and said filaments through said spin bath, PA1 (v) extracting said lyocell filaments in the form of a tow through a hole in the lower portion of said spin bath, said hole being provided with a resilient periphery to be resiliently urged into contact with said tow, and PA1 (vi) maintaining the length of the strands in the air gap in the range 0.25 to 50 cm.
(1) an "organic solvent" means essentially a mixture of organic chemicals and water; and PA2 (2) "solvent spinning" means dissolving and spinning without the formation of a derivative".
Thus a lyocell fibre is produced by the direct dissolution of the cellulose in a water containing organic solvent--typically N-methyl morpholine N-oxide--without the formation of an intermediate compound. After the solution is extruded (spun) the cellulose is precipitated as a fibre. This production process is different to that of other cellulosic fibres such as viscose, in which the cellulose is first converted into an intermediate compound which is then dissolved in an inorganic "solvent". The solution in the viscose process is extruded and the intermediate compound is converted back into cellulose.